Field of the Invention
The present invention relates to a numerical controller, a control system, a control method, and a control program for controlling multiple machine tools in a series of steps.
Related Art
A numerical controller (CNC device) as an electronic device for controlling a machine tool controls various motors by mainly following a machining program and various parameters to realize machining. More specifically, a motor is used for rotating a spindle to which a cutting tool is attached and rotating an axis for moving a table, etc. where a workpiece is fixed.
A large number of machine tools are installed in a factory as an actual machining site, and each of the machine tools is responsible for machining on various parts. In some cases, multiple machine tools work sequentially for machining on one part. For production of one item, various steps to be done in a factory are prepared, and a time from the start of machining to the completion of the item differs between parts and between the steps. Hence, the processing capacity of the factory as a whole is evaluated in terms of throughput showing processing capacity with which a completed item is produced per unit time.
Throughput is affected not by the length of time from the start to the end of machining but by a bottleneck that is a step taking the longest processing time. Even if production activity in a step not causing a bottleneck is done until the capacity of a factory reaches its limit, process cannot be progressed in the factory as a whole to an extent exceeding a limit of a bottleneck. This causes redundant intermediate materials during the course of production of a completed item or shortens the operating time of a machine tool in a step executed after a bottleneck step. A method of making a production plan for step optimization has been suggested as a technique allowing for a bottleneck (see Patent Documents 1 to 3, for example).
Patent Document 1: Japanese Unexamined Patent Application, Publication No, 2004-30199
Patent Document 2: Japanese Unexamined Patent Application, Publication No. 2004-145436
Patent Document 3: Japanese Unexamined Patent Application, Publication No. 2012-243894